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Hugh Pickens writes "No two subway systems have the same design. New York City's haphazard rail system differs markedly from the highly organized Moscow Metro, or the tangled spaghetti of Tokyo's subway network. Now BBC reports that a study analyzing 14 subway networks around the world has discovered that the distribution of stations within each of the subway networks, as well as common proportions of the numbers of lines, stations, and total distances seem to converge over time to a similar structure regardless of where the networks were, when they were begun, or how quickly they reached their current layout. 'Although these (networks) might appear to be planned in some centralized manner, it is our contention here that subway systems like many other features of city systems evolve and self-organize themselves as the product of a stream of rational but usually uncoordinated decisions taking place through time,' write the study authors. The researchers uncovered three simple features that make subway system topologies similar all around the world. First, subway networks can be divided into a core and branches, like a spider with many legs. The 'core' typically sits beneath the city's center, and its stations usually form a ring shape. Second, the branches tend to be about twice as long as the width of the core. The wider the core, the longer the branches. Last, an average of 20 percent of the stations in the core link two or more subway lines, allowing people to make transfers. 'The apparent convergence towards a unique network shape in the temporal limit suggests the existence of dominant, universal mechanisms governing the evolution of these structures.'"

The first subway I tried was in Berlin, Germany and it was somewhat daunting experience for someone who hadn't got used to the system. Previously I've only used systems where you pick what you want and get it.

But now there was tons of choices and moving around to get the whole trip finished. The lady over the counter would ask me tons of questions - like do I want white italian, parmesan & oregano, wheat or sesame bread. Southwest sauce, sweet onion, barbecue sauce or light mayo. Cheddar cheese, onions, lettuce, pickles, green peppers, jalapenos, with a choice of meat. Like pepperoni, salami, tuna, chicken, roast beef, meatballs, steak and cheese... ham or spicy italian... do I want extras like double cheese or bacon? Did someone say double bacon? Footlong or 6-inch...

The system greatly confused me. But being a warrior of food, I survived. I got my delicious subway. And you know what? Ever since I've loved subways. It is absolutely delicious. Chipotle southwest with ranch or light mayo is the ultimate sauce. What I cannot, however, understand is why would anyone put MUSTARD on a subway?

Interesting story regarding pizzas, sandwiches and subways by the way. My old girlfriend used to LOVE tuna subways, while I only ate ham & cheese. She always laughed about it and told me to try something new. Too bad I didn't. But a few years later, I hit the wall. I could not eat anymore ham on pizzas or subways. It just started to taste like shit. I don't know why. But then I discovered the magical taste of tuna subways and pizzas along with salami and pepperoni and bacon. So for all of you who only eat one kind of ingredient all the time - do try something new. You only have one life to enjoy!

Exactly. It's obvious that e.g. distances between stations can't be too short or too long. And obviously the structure is determined by the structure of the city, the distribution of its population and their destinations. And subway planners might also have taken a look at solutions in other cities. I think I'm going to do a study on mathematical properties of articles in the Journal of the Royal Society Interface. I will of course assume that such articles are self-organizing, and arrive at the surprising conclusion that they're all made up of words; I might even find that some words are much more frequent than others, despite there being so many opportunities in so many different pieces of text. I expect this conclusion to reach Slashdot in due time...

Moscow metro is like they describe, a centre core, and legs out in all directions. However, there is a larger ring, outside the 'natural core' that is caused by crossing lines.

The (presumably apocryphal) story goes that... The designers brought the plans for the Metro expansion to Stalin. He had set a coffee cup on it, and left a coffee ring around the centre. None of the engineers were willing to go against what could be perceived as Stalin's 'edit', so the coffee ring was built.

(It's always coloured brown, on maps of the metro. It's kind of cute...)

But did you notice the mathematical trend between the subways you visited? In every one, there was a number of bread containers for said subway. Within that container, there was a number of items which could be placed within it. And finally, and the clearest proof intelligent design is behind subway is that, at the end of the subway assembly, a numeric value was placed upon it, to which you were required to tender local currency or suitable plastic representation, to take possession of your tasty meal.

The tasty meal part isn't necessarily proven. That would depend on what you had put on it.

I could really use a meatball sub with extra sauce. Damn you, Subway, why don't you have a location near me open 24 hours? I'd even be willing to take a subway to the Subway, so I could enjoy my Subway sub, except there is no subway close to me to take to the Subway.